Neurotransmitters and hormones are released by Ca2+triggered exocytosis, whereby a vesicle fuses with the plasma membrane of a cell and expels its content into the extracellular space. This project has focused on the fusion pore, the initial fluidic passage between the vesicle interior and the outside of a cell. Studies of the fusion pore have given us valuable insights into the mechanism of exocytosis and the roles of specific molecules in the regulation of membrane fusion. The previous funding cycle made progress in identification of some of the fusion pore-forming proteins, and developed new techniques that will allow us to achieve these goals more effectively. We will use these new methods to perform definitive experiments on the role of synaptobrevin, a key protein involved in exocytosis, and determine whether synaptobrevin is a structural component of the fusion pore. Parallel studies of fusion pore manipulations between the PC12 cells, chromaffin cells, and neurons from the brain will define how fusion pore function influences the speed of neurotransmitter release at synapses. New results on membrane elasticity and exocytosis have allowed us to expand the scope of this study and determine how proteins can induce curvature in lipid membranes in order to shape and remodel them. Finally, experiments in PC12 cells and chromaffin cells will test a new theory that energy stored in helix-coil junctions serve as a driving force to bend membranes.